LonCray
I wonder why it's always mad scientists? Why not mildly angry scientists?
English is a strange language, doubly so for its native speakers.
"Mad Scientists" are mad like "Hatters" are "mad."
In the olden days of haberdashery, quicksilver (e.g. mercury) alloys of inexact proportion to work felt for hats. Mercury toxicity then produced mental abberations which were collected under the single category "mad."
OED tells us "mad" comes from Old English from Germani "gemäd" (ghe MAYD). The connotation of "mad" as angry reflects the split between British and American English useage. Although popular culture references have passed the mad = angry connotation back to Blighty. There's at least one refernce that avers that the "mad as angry" gets its origin from forms of "temporary insanity," which may have been manic episodes of bipolar disorder.
But, English is complicated that way. Try explaining "Throw the rough bough through enough into the rouge slough" to an non-English speaker.